1. Field of the Invention
The present invention relates to a method of manufacturing an electronic circuit and a manufacturing apparatus of an electronic circuit.
2. Description of the Related Art
Conventional manufacturing methods of circuit boards are largely classified into the following two methods: (1) a subtractive method and (2) a build-up method.
(1) The subtractive method is a method in which a substrate constituted of, for example, a copper (Cu) foil and an insulating layer bonded together is subjected to steps of resist coating, exposure, developing, Cu foil etching, resist removal, and so on in sequence, thereby forming a conductor pattern.
(2) The build-up method is a method in which an insulating layer forming step including steps of bonding a photosensitive resin layer, exposure, developing, etching, and so on and a conductor layer forming step including steps of metal thin film forming, resist coating, exposure, developing, plating, resist removal, and so on are alternated, thereby forming a multilayer circuit.
In both of the methods, however, the need for forming masks used for exposure in advance has caused cost increase and long time for designing and preparing the masks. In addition, the cost and delivery time of the circuit board have been greatly influenced by the correction of the masks, if the need for the correction should arise.
In recent years, new methods of forming circuits by electrophotographing (disclosed, for example, Japanese Patent Laid-Open Application No. 2001-284769) have been provided in place of the abovementioned methods. In these methods, an image of electric charges (electrostatic latent image) in the shape of a circuit pattern is formed on the surface of a photosensitive base, and after charged particles for circuit formation are brought into electrostatic adhesion with this electrostatic latent image, a visible image made of the charged particles is transferred onto a ceramic green sheet, and thereafter fixed by heat.
With such electrophotography, however, it has been impossible in principle to impart an electrostatic property to conductive particles. It is barely possible to impart the electrostatic property to a metal oxide film, but the formation of a conductive pattern has been difficult due to extreme difficulty in adjusting the thickness and quality of the oxide film and controlling the quantity of electric charges.
Therefore, a method has been proposed such that an insulative resin as a binder is mixed with metal particles and a charge control agent or the like is added to the mixture, thereby balancing an electrostatic property and conductivity.
However, in a pattern formed by this method, due to the existence of the insulative resin serving as the binder among the metal particles, an electrical resistance value is higher by about three digits than that of a typical circuit board in which a highly conductive metal such as Cu is used as a wiring conductor. Therefore, the use of this pattern as a wiring circuit has not been possible.
Further, in the circuit pattern formed on the ceramic green sheet by the aforementioned method, though the electrical resistance can be lowered to some extent by removing the binder resin by burning, it has been still impossible to obtain sufficient electric conductivity as a wiring circuit. In addition, the removal of the binder resin by burning is a technique limitedly used for ceramic substrates and cannot be adopted for substrates in which resin such as epoxy resin is used as a base material.
Moreover, as for the composition of the charged particles for circuit formation, the content of metal particles needs to be increased in light of electric characteristics. However, conductivity and imparting of the electrostatic property are in a trade-off relation, which has posed such a problem that the increase in metal particle content results in difficulty in controlling the electrostatic property. Therefore, the metal particle content needs to be adjusted to balance the electrostatic property and conductivity. Especially, in order to form a microscopic pattern such as a circuit pattern with high precision, controlling the electrostatic property is extremely important, but the industrial production of conductive resin which can achieve both high precision in circuit formation and good electric characteristics has been extremely difficult.
As a method of overcoming this problem, Japanese Patent Laid-Open Application No. Hei 8-56077 discloses a method of forming a circuit selectively by etching after forming a pattern of an etching resist on a metal film by electrophotography. This method is advantageous in that conductivity in a conventional resin substrate can be ensured since this method can use a copper clad laminate or the like which is made by bonding a Cu foil on a base material such as glass epoxy.
In this method, however, it has been necessary for a resin material for pattern formation to have not only an electrostatic property necessary and appropriate for electrophotography but also etching proof indispensable as a resist and removability after etching. Moreover, this method has not been able to fully satisfy demands such as cost reduction and a shorter cycle of design, production, and so on.
An object of the present invention is to provide a method of manufacturing an electronic circuit and a manufacturing apparatus of an electronic circuit that can fully satisfy demands such as cost reduction, diversified small-quantity production, and a shorter cycle of design, production, evaluation, correction, and so on.